357AR

Here is what I've been working on this past winter with a lot of imput with several members over at weaponsguild. An ar15 based off of a 357 maximum rimless loaded to 223 pressures. I started with a home made chamber reamer (because standard 357max reamers won't work) and a 357 test barrel and once I got the bugs worked out I sectioned the test barrel and bought a Green Mountain blank to turn down. I haven't run it over a chronograph yet, but I was able to go above what Quickload shows for a 158gr bullet @ 2250fps without any signs of high pressure. I'm currently working up loads for 180gr bullets. Here's a few pics.

"If they’re going to come here illegally, apply for & receive assistance through a corrupted Government agency encouraging this lawless behavior, work under the table & send billions of dollars each year back to their families in Mexico, while bleeding local economies dry, protest in our streets waving their Mexican flags DEMANDING rights, while I have to press ’1′ for English, then they need to be shipped back to where they came from!" -Chad Miller

Thanks 2nd! It was a fun build. Hopefully I'll get a chance to try it out on a deer this year. I also plan on turning the left over barrel blank into a pistol upper chambered for it as well once I finish a 80% lower so I have a pistol lower. I still should be able to get near 2000fps with 158gr bullets and a 9.5" barrel.

I was looking around for info on this build 6-8 months ago before i went 300 black out. Is there a reference web site on ar 357's??

Nope! I found info about making a rimless 357 mag, but the only info I could find about a 357 max rimless in an AR15 was that "it can't be done" because of the length The length was actually only a minor problem. I have two threads about the build concept and actual builds at weaponsguild. I tried using modified 357 max brass at first, but soon found out that they aren't a good canidate because although the web is higher on the max case the case wall is thinner since it is meant to be completely inside the chamber except for the rim, where the 223 case has a slightly shorter web with noticably thicker walls to handle the case sticking an 1/8" out or so. Once that was decided upon I did stick with the 357 max case length which gives you a very close case capacity to a 357 maximum. Mad Machinist suggested 357AR for a name and it stuck. I suppose it does sound better than 357 MoleMan Magnum
I found info on 357 maximum loaded to 223 pressures in strong actions with longer barrels which gave me hope of a real deer thumper which I think I've obtained. I haven't started playing around with powders and have been using 2400 and should be able to increase the velocity a bit switching to 296 or H110. I'm still working on 180gr loads, but the Hornady 180gr SP SSP Interlock looks to be very good. I was able to get blunt 158gr SJHP bullets to feed well and also 200gr rn bullets, but the pointy 180gr hornadys feed smoother. The 357 Maximum is a hot round, but the pressure is limited because not all of the firearms chambered for it (like revolvers) are strong enough to handle the increased pressure. The AR15 is meant for higher chamber pressures and since it has a larger bore diameter the pressure drops off faster than a 223. Modifying 223 cases was an issue at first, but I've figured out how to bump the cases up to straight wall with acceptable case losses which is bound to happen with that dramatic of a change in diameter.

j427x, this is basically a hot 357 max even though the cases are formed from a 223 case the case capacity is within 1/10th of a grain of water between a modified remington 223 case and a remington 357 max case which is less than some cases will vary between brands. 357 max dies and reloading data can be used, and you can work up loads hotter than what the max stops at in the reloading books although some tc data is close. Look through the reloading data and velocities on this site and the links to load work-ups if you have time 357 Remington Maximum Loading Data
Check out the velocitys listed, but keep in mind it is with a 24" barrel. I don't know how much of an advantage the extra length gives him since the majority of the velocity is acheived in the first 10" at which point the velocity arc isn't as great. Here's a quickload graph Zebdeming made for my test barrel which was 17". I ran out of 158 gr bullets and moved on to .358" 180gr bullets which I started getting signs of increased pressure at 20.5gr- 21.0gr, so I backed down to 20.0gr in the test barrel which was a generic 9mm/38 bore diameter. My new barrel is a .358" blank with a 1-14" twist since I plan on mostly shooting bullets 158gr and heavier.

Interesting huh? I don't plan on ever putting a 24" barrel on an ar, but even taking a couple hundred fps off for a shorter barrel is still nothing to sneeze at. The pressure graph above is for Alliant 2400 which is a good powder, but isn't the best choice for this round if you're wanting more velocity. I picked up some 158gr XTP so I will try them out as well.

INTERESTING looks like you put a lot of work into developing it. it should do well on deer.

a littel off topic but I have turned a barrel tuned for a 358 win AK47. wanted the same thing heavier bullet with good speed. if I was confined to a ar length magwell id be really interested in you round. I have a 223 ak that the barrel is not the best and that would be a cool barrel swap only round for it. HMMMMMMM

your round would likely be good loaded subsonic as well. the round is kind of like the 9mmx39 just a little smaller.